It is known as from U.S. Pat. Nos. 3,587,618, 3,595,559, 3,628,758, 3,693,915, 3,710,549, 3,732,668, 3,788,039, 3,788,040, and 3,830,307 to provide a vent valve, relief valve, or combination vent and relief valve in conjunction with an aircraft fuel tank inerting system in which an inert gas, such as nitrogen, is employed to pressurize the fuel tank and to maintain the oxygen content of the ullage gases at a level to prevent fire and explosion. Heretofore, such combination vent and relief valve, also commonly referred to as a climb and dive valve has comprised separate valve elements of which the vent valve element opens as during descent of the aircraft to admit ambient air into the fuel tank in the event of insufficient rate of flow of inert gas into the fuel tank, and of which the relief valve opens as during ascent of the aircraft to prevent the tank pressure-ambient pressure differential from exceeding a predetermined value.